The present invention relates to devices exhibiting a variable transmittance of light and radiant heat, and in particular to such devices which are substantially solid state in nature.
In bright sunlight, closed edifices made primarily from glass and buildings having numerous glass windows experience heat buildup due to the transfer of heat from the sun through the glass via radiation. Heretobefore, glass has been coated by some means to prevent this heat transfer. For example, greenhouses, especially the roof areas thereof, are sprayed with white or green pigment thereby reducing light transmission and the corresponding heat buildup. Application of pigment is difficult, must be repeated at regular intervals, and leaves an aesthetically undesirable appearance. More importantly, although light and radiant heat transmission can be desired at various times, pigmentation permanently reduces the transmission of heat and light.
More recently, various attempts have been made to provide devices capable of providing a variable transmittance of light and radiant heat. For example, reflective-transparent solar control films can be coated onto glass as described in U.S. Pat. No. 3,290,203. However, as noted in U.S. Pat. No. 4,260,225, such a device suffers numerous deficiencies. In addition, U.S. Pat. No. 4,260,225 discloses deficiencies of permanently transluscent plastic films which replace glass in greenhouse covers.
Energy saving devices are disclosed in U.S. Pat. Nos. 4,260,225; 4,085,999; 4,082,892 and 4,307,942. Such devices typically comprise light transmissive (i.e., transparent) layers which enclose a region containing a polymeric material which is capable of transmitting light at one temperature but which becomes less transparent at another temperature. Thus, such devices are believed to result in energy savings because radiant heat energy is transmitted through the device to a much less extent at higher temperatures.
Although such systems provide an effective means for preventing unwanted heat from entering a building, such systems are severely limited in their practical use. For example, exterior portions of buildings are frequently exposed to severe weather conditions, and in particular are exposed to temperatures as low as about -50.degree. F. Unfortunately, devices containing the aforementioned polymeric materials are susceptible to freezing which causes cracking or other destruction of the device. In addition, wide fluctuations in temperature, particularly temperatures above the cloud point of the polymeric material cause settling problems of the active polymeric material.
More recently, as disclosed in U.S. Pat. No. 4,260,225 energy saving radiant insulative devices contain water-soluble polymers which exhibit an inverse solubility with an increase in temperature, water and an organic liquid which lowers the freezing point of the polymeric fluid system. Unfortunately, such systems require polymeric fluids which have a high polymer concentration and exhibit a high viscosity. Such high viscosity systems are often difficult to handle and can often introduce undesirable air bubbles into the polymeric fluid system. In addition, the addition of various organic liquids such as glycols in certain amounts to such polymeric fluid systems do not necessarily allow the desired change in transmittance of radiant energy in the desired temperature range. For example, polymeric fluid systems containing certain glycols may provide low radiant energy transmittance over an undesirably wide temperature range, or may provide little or no decrease in radiant energy transmittance over a wide temperature range. In addition, fluid-based systems are difficult to handle and provide problems in the manufacture of energy saving radiant energy insulative devices. Furthermore, fluid-based systems can provide problems associated with glass pane breakage, particularly when large radiant energy insulative devices are manufactured.
Various transparent-translucent materials are disclosed in U.S. Pat. Nos. 4,409,383; 4,444,846 and 4,206,980. However, it would be desirable to prepare substantially solid state thermal radiation suppressor compositions using effective and efficient techniques.
In view of the deficiencies of the prior art, it would be highly desirable to provide a practical device for inhibiting the transmission of solar energy above a predetermined temperature range, but which permits transmission of said energy below that temperature range, which device comprises substantially solid state temperature sensitive substances contained in said device.